1. Field of the Invention
This invention relates to air-breathing solid fuel rocket motors. More particularly, this invention relates to solid fuel ramjet grains having a plurality of concentric layers of solid ramjet fuel. Even more particularly, this invention relates to a method of controlling thrust in a solid fuel ramjet.
2. Description of the Prior Art
It is well known to vary the thrust of solid composite rocket motors by using multiple concentric layers of propellants. The propellants in these rocket motors contain sufficient oxidizers to support complete combustion without additional air. It is possible to vary the thrust of the solid composite rocket motor by varying the combustion properties for each concentric layer of propellant.
It is also known to use multilayer propellant designs with an inert liner material between the layers which has insufficient incorporated oxidizer to support combustion. After the initial layer of propellant material burns through, the rocket ceases to function. However, if additional impulse is needed to extend the range of the rocket, an oxidizer fluid which is hypergolic with the liner is injected into the chamber igniting the liner which after burning through, ignites the adjacent layer of propellant.
The two previously described systems which use multilayer propellant arrangements operate in a different manner from air-breathing solid fuel rocket motors because prior art solid composite rocket motors contain sufficient oxidizers to support complete combustion. As a result, complete combustion occurs in an area partially defined by the surface of the propellant grain. On the other hand, the solid fuel of air-breathing solid fuel rocket motors undergoes combustion only after mixing with air ingested from the atmosphere. Combustion occurs at the fuel grain surface and in combustion after chamber to produce thrust.
Existing solid fuel ramjet motors utilize one fuel of a homogeneous compostion which burns to produce a relatively constant thrust until burn-out. The limitation with single-fuel ramjet systems is that such systems are only able to produce a single level of thrust.
Previous methods of controlling the thrust produced by air-breathing solid fuel rocket motors operated by controlling the flow of ram-air to the engine. These methods have had limited success because they interfere with the stability of air flow into the motor necessary for proper operation of an air-breathing rocket motor. As a result, it is extremely difficult to throttle a solid fuelled air breathing system. The present invention provides a passive form of throttling without affecting the air flow.